Converting DC points operation to include DCC. operation...

[RAF96]

Do you currently use analogue points motor operation selected say by pen and stud, push button switches, etc, but would like the option of having DCC points operation say to be able to use routing in a pc software application like JMRI or Rocrail, etc, without having to totally rewire.

 

Well thanks to an idea that Lester ( http://www.modelrailaway.co.uk/ ) passed to me you can. You use the DCC accessory decoder simply to pulse the pull-in-coil of a car headlight flasher relay that fires your CDU to the point motor just as if you were making the selection yourself. Brilliant idea Lester - it works exactly as you said it would.

 

The attached wiring diagram shows how the additional wiring integrates into my system, which uses 3 x rotary switches (RSw) and 2 x push buttons for each RSw to fire 15 out of a possible 18 point motors.

 

You can see how easily it will integrate into your system. The DCC accessory decoder fires a pulse to the pull-in-coil of 1 of 2 relays (1 for straight and 1 for turn). Each relay is fed power from the CDU positive output and passes it to either the straight or turn side of the point motor as wired - just a short burst same as a push button or passing switch contact provides.

 

There is no need even to worry too much about getting the orientation of which relay fires which side correct as most software programmes allow you to invert the motor selection on screen to avoid rewiring.

 

You will need a lot of relays (I used 30) as there are 2 per accessory decoder port, so 8 per Hornby accessory decoder, but they are cheap as chips at under £2 each (single pole normally open contacts).

Edit: Probably the cheapest place would be your local car breaker/scrapyard.

 

So if you want the best of both worlds for your points motor operation give it a try and thanks once again to Lester for the original idea.

Robbie

 

[melmerby]

You use the DCC accessory decoder simply to pulse the pull-in-coil of a car headlight flasher relay that fires your CDU to the point motor just as if you were making the selection yourself.

 

I think I get what you mean but how about this way:

 

Use a semiconductor (Mosfet) operated by the pulse from the accessory decoder to operate the CDU/coil, rather in the way some of the accessory decoders with built in CDU do.

Would need a couple more components e.g. diodes etc. to finish the circuit. IMHO much smaller, neater and probably cheaper (unless you have loads of cheap relays!)

 

Keith

[RAF96]

Hi Keith

Feel free to amend the diagram to reflect your suggestion. I can let you have the original which was done in Excel if required.

Robbie

[RFS]

I use Lenz LS150 accessory decoders to fire my Peco PL10 point motors. With the output being 3 amps @ 15 volts AC they all fire reliably without the use of a CDU, which you can't have anyway with the LS150. Some other makes of accessory decoder do include a CDU however.

 

The LS150 also supports connection to push buttons so you can have both a manual control panel as well as operation from your DCC throttle or a computer. I do not know if other accessory decoders support this manual operation and can only be operated via a DCC command, which would mean they couldn't be used in this set up. But if you fire the accessory decoder from a manual push button, the change is not sent across the DCC control bus, so any computer software will not be aware of the change and its display of the layout will be wrong. This is certainly the case with my LS150s and RR&Co's Trancontroller software - hence I don't use separate push-buttons. The major benefit of using a computer to operate points is that you always have a clear display of which way the points are set.

 

But I would look at the costs: say £4.50 for a PL-10, £2.50 for a PL-13 accessory switch (I would assume with DCC you are using switched Electrofrog points) and £4 for two relays brings that to £11 per point not including any wiring, terminal strips and the cost of a CDU. For this outlay you still have a solenoid point motor with all its limitations, but for roughly the same money (or a couple of pounds more) you can purchase slow-action point motors instead. DCC Supplies sell Fulgrex ones for £9.71 and Tortoise for just under £14 if bought in a 6-pack.

[buffalo]

...The major benefit of using a computer to operate points is that you always have a clear display of which way the points are set...

 

A little over-confident, methinks Without some form of detection system, all you get is the software's best guess at which way the turnouts are set. If the software starts up thinking the turnouts are set differently to reality, or if a motor fails to throw, the information you get is no better than any other method of indication.

 

Nick

[Nigelcliffe]

The LS150 also supports connection to push buttons so you can have both a manual control panel as well as operation from your DCC throttle or a computer. I do not know if other accessory decoders support this manual operation and can only be operated via a DCC command. But if you fire the accessory decoder from a manual push button, the change is not sent across the DCC control bus, so any computer software will not be aware of the change and its display of the layout will be wrong. This is certainly the case with my LS150s and RR&Co's Trancontroller software - hence I don't use separate push-buttons. The major benefit of using a computer to operate points is that you always have a clear display of which way the points are set.

 

 

The lack of communication from local buttons is a limitation of the LS150, or the Lenz bus architecture.

 

 

On other architecture's, feedback from local push buttons to the central command station (and computer) are part of the design. Digitrax' LocoNet does this, and I think other solutions such as S88 can do it. With LocoNet, the messages are the same - "set turnout 123 to thrown" - regardless of whether its generated by a throttle, computer or local push button.

Consequently, its not difficult to build systems with real button switch panels which interwork with a computer running RR&Co TrainController and conventional hand throttles - human panel users can select routes/blocks which in turn cause TrainController to hold trains at signals pending the route being cleared ahead, etc...

 

 

 

- Nigel

[RFS]

A little over-confident, methinks Without some form of detection system, all you get is the software's best guess at which way the turnouts are set. If the software starts up thinking the turnouts are set differently to reality, or if a motor fails to throw, the information you get is no better than any other method of indication.

 

Nick

 

I agree - it's all down to having reliable point motors and not changing the points when the computer is down, or the control program is not running. I have 70+ point motors with RR&Co software and I rarely have a problem in this respect. If a PL-10 doesn't throw for any reason you get notification of this - silence!

[melmerby]

Hi Keith

Feel free to amend the diagram to reflect your suggestion. I can let you have the original which was done in Excel if required.

Robbie

 

Hi Robbie

The idea you presented is elegant in its simplicity but the thought of using all those car relays gave me the idea based on what I need to do to operate some H&M point motors from LS150s (mentioned above re PL10s).

 

I am a bit of an experimenter by nature and it would depend on the output from the accessory decoder and the polarity of the CDU, exactly what would be needed, I would try a set up on the bench before committing it to a PCB or whatever.

 

It was a suggestion as to another possible way of doing it, based on the circuitry I have seen in DCC/CDU combined accessory decoders.

 

I have LS150s operating Seeps at the moment and they seem pretty reliable, but I have tried to use them with my H&M point motors and the H&Ms are a bit iffy, although they will operate everytime from a CDU with about 15v DC and a big capacitor.

 

Keith

[melmerby]

 

 

The LS150 also supports connection to push buttons so you can have both a manual control panel as well as operation from your DCC throttle or a computer.

 

 

If you are referring to the diagram in the LS150 manual, it is not part of the LS150 operation, the push button is just in parallel with the triac switch.

 

But I would look at the costs: say £4.50 for a PL-10, £2.50 for a PL-13 accessory switch (I would assume with DCC you are using switched Electrofrog points) and £4 for two relays brings that to £11 per point not including any wiring, terminal strips and the cost of a CDU. For this outlay you still have a solenoid point motor with all its limitations, but for roughly the same money (or a couple of pounds more) you can purchase slow-action point motors instead. DCC Supplies sell Fulgrex ones for £9.71 and Tortoise for just under £14 if bought in a 6-pack.

 

Or buy a Traintronics TT300, it can be got for about £18-£19 and includes the decoder with route setting possibilities. Will work on DC as well, makes the Tortoise look a tad expensive and oversize.

 

Keith

[melmerby]

Hi Keith

Feel free to amend the diagram to reflect your suggestion.

 

Hi Robbie

What do you think of doing it this way?

 

I have had another look and I would have to turn the circuit as drawn on it's head so that the +VE from the CDU goes to the common on the coil and the coils (straight and turn) would return via the switch and buttons to the -VE.

 

I am assuming the accessory decoder being used gives a pulse which is +VE compared to it's common connexion (not an LS150 which is AC!)

If you connect the common from the accessory decoder (which must be powered from a separate supply) to the CDU -VE a suitable mosfet could be connected with the source to -VE and drain to coil with it's gate connected to the +VE output of the accessory decoder (probably via a resistor). Diodes would be need to be provided across the coils to act as spark quench so that any BEMF does not destroy the mosfet.

You may need to provide a dummy load (resistor) across the accessory decoder output which might not work reliably with a high impedance across it.

 

The only obvious problem I can see is the possibility that you cannot connect different commons on the accessory decoder together. If that is the case you start getting into the realm of opto-couplers which means it is getting over complex.

 

Keith

[Suzie]

The lack of communication from local buttons is a limitation of the LS150, or the Lenz bus architecture...

 

- Nigel

 

Lenz architechture does feedback via the RS bus. The command station (LZV100) takes the feedback from the RS bus and puts it on to the ExpressNet. It is slightly different to the way Digitrax do it on Loconet but the result is the same - your software just queries the ExpressNet to get the status of the point from a feedback module. Feedback can be from the point position via a microswitch so even hand operation can be fed back.

 

 

Loconet makes the hardware implementation easier for getting feedback from local buttons though, no need to connect up an extra bus.

 

 

[RAF96]

Thanks for the feedback people. A lot of good alternative ideas there.

 

The important thing is expense. Yes - if you are doing it from scratch then it is heavy on the pocket and other point motors and signal devices become equally if not more cost effective.

 

I already had all the track, all the point motors and the rotary and push button switches existing from my old layout, so the only new expense I had was for the relays. These cost £1.50 each new from Maplins when bought in quantity (I needed 30), but you could probably get them for a few pence each at your local car scrappie. They are simple 12v single pole 4/5 pin relays such as used for headlight flasher (4 pin) or circuit chage over (5 pin). Obviously there are more compact PCB relays and more electronic method solutions to the problem, but I worked with what I am happy with and understand well. I know a mosfet from a darlington pair but I was half way there with my existing mechanical kit.

 

The new layout had the manual points operation system installed, then I got re-interested in Rocrail with its ability to analyse your trackplan and figure out all possible routes, then set the points (must be DCC points) either which way in sequence as required, so I had to work out how to have DCC point operation in parallel with my exisitng manual system.

 

In answer to Keiths Q's about polarity - yes you can swap pos and neg around on both the DCC side and the solenoid side, but what you must not do is let the solenoid CDU side get anywhere near the DCC acc decoder side.

 

I haven't pulled a Hornby acc decoder to bits to see whats in there but I doubt if you can wire all the commons together to a bus. My method just commons the 2 relays on any 1 port.

Thanks for the interest and I look forward to seeing what else pops up.

Robbie

[melmerby]

 

In answer to Keiths Q's about polarity - yes you can swap pos and neg around on both the DCC side and the solenoid side, but what you must not do is let the solenoid CDU side get anywhere near the DCC acc decoder side.

 

I haven't pulled a Hornby acc decoder to bits to see whats in there but I doubt if you can wire all the commons together to a bus. My method just commons the 2 relays on any 1 port.

Thanks for the interest and I look forward to seeing what else pops up.

Robbie

 

There should be no problem with doing what I said as long as the two devices have a separate supply and the commons are just that. The pulse from the CDU does not get to the output of the accessory decoder. Ideally you would use an opto coupler for total isolation but that adds to the complexity.

On the LS150 the commons are all connected to the LH AC input. That's why you can bridge the outputs with a switch for manual operation, as per RFS's comment.

You could of course use the AC from a LS150 but it would need a diode (& possibly capacitor) to produce the DC component to switch the mosfet. (I intend trying that myself to operate my H&M motors)

If a DC output device has the same arrangement connecting the commons to the -ve CDU supply will work.

 

Keith